This invention relates to the field of secondary or rechargeable batteries and the arrangement of such batteries to achieve improved electrical and physical characteristics capable of use as an electrical filter element and in other energy storage uses.
In space satellite vehicles and other volume limited and weight limited environments wherein a pulsating load current and a pulsed source of electrical energy or a source of electrical energy of limited current delivering capability are to be married into a direct current operated system, the need arises for an energy storing electrical filter element of higher energy density capability than has been heretofore available--an energy storage density of significantly improved capability with respect to the conventionally used electrolytic capacitor. In space satellite vehicles of relatively large electrical energy size, weight savings in the order of 5,000 lbs together with significant volume savings are envisioned with use of the improved electrical energy storage arrangement afforded by the present invention battery filter element.
The conventional electrolytic capacitor is usually operated under energy storage conditions which achieve about 1 joule of electrical energy storage per pound of capacitor weight. Conventional nickel-cadmium batteries when used in lieu of such electrolytic capacitors in power supplies are found capable of energy storage densities as high as 10 joules per pound. The presently disclosed battery filter element, in contrast, is capable of operation in the 40 joules per pound storage density range with the suggestion of even larger energy per pound operation.
For electrical waveform filtering and for use in small size, low electrical impedance power supply sources, a form of secondary cell or rechargeable battery known as the bipolar electrode battery is considered especially attractive. In a bipolar battery the positive electrode of one battery cell and the negative electrode of the adjacent battery cell are formed on opposite sides of the same plate or substrate member. A battery of such cells is therefore comprised of a plurality of these bipolar plates with each plate face being exposed to a segregated quantity of battery electrolyte--electrolyte also exposed to the next plate of opposite polarity in a battery array of cells. The necessary segregation of adjacent cell electrolyte quantities, however, provides one of the principal disadvantages of such a bipolar battery structure, i.e., the effective and permanent segregation of adjacent electrolyte quantities, particularly at the periphery of a bipolar electrode plate has proven to be a difficult accomplishment. Despite this significant practical problem the low cell interconnection resistance and inductance and the low intra-cell impedances of the bipolar battery are attractive for many uses, including the filtering needed in a power supply. In the bipolar cell, the relatively large surface areas contribute to low cell interconnecting resistance and to small electrode to electrolyte resistances. The large areas and short direct cell interconnections also afford light weight and small size for a given cell electrical capacity. The low interconnecting resistance is at least in part attributable to the absence of separate cell interconnection conductors such as the familiar straps between cells in the six-volt automobile storage battery. In the bipolar battery structure, cell interconnection occurs between the oppositely polarized sides of a given battery plate member, that is, between the positive electrode material on one side of a plate structure and the negative electrode material on the opposite side of a plate structure.
The sealing of a bipolar electrode plate against electrode leakage between adjacent cell electrolyte quantities is a complex problem involving such considerations as plate dimensional change as a result of battery temperature change, molecular transfer of electrolyte through the porous paste layers of an electrode in the case of paste electrodes carried on a wire mesh or other permeable substrate structure, and relatively large plate and seal dimensions--on the order of three-inch plate diameter for a battery of moderate current delivering capability and life. The sealing also involves a dense liquid electrolyte of significant wetting property and high chemical activity--electrolytes of such solutions as sulfuric acid and potassium hydroxide are commonly employed, and also requires practical and easy manufacture without the use of tedious, long-duration seal achieving fabrication steps.
Additional information concerning the bipolar battery and also information concerning the construction, testing, and characteristics of the semi-bipolar battery of the present invention are included in a technical report titled "Pseudo-Bipolar Nickel-Cadmium Batteries used as Filter Elements to Pulsed Current Loads", AFWAL-TR-84-2094, written by Michael B. Cimino and Gregory M. Gearing of the Energy Conversion Branch, Aerospace Power Division, Aero Propulsion Laboratory, Air Force Wright Aeronautical Laboratories, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio, 45433. The Cimino-Gearing technical report is unclassified and unrestricted in distribution and is available from the above address, and from the National Technical Information Service. The disclosure of this report is also included in a thesis submitted to the Air Force Institute of Technology, Wright-Patterson Air Force Base, Ohio, 45433 in partial fulfillment of the requirements for the Master of Science Degree. The substance of the AFWAL technical report, the Air Force Institute of Technology thesis and the disclosure of the copending patent application "Power Supply Filtering With Rechargeable Battery Element" referred to above are hereby incorporated by reference into the present specification. An article referenced in the AFWAL technical report. "Batteries for Space Power Systems", written by P. Bauer of the National Aeronautics and Space Administration in 1968, NASA SP 172, provides additional details of the bipolar battery and additional background information regarding batteries suitable for use in satellite vehicles and other space hardware. The Bauer article is also incorporated herein by reference.
The battery of the present invention approaches the advantages of the bipolar battery while also providing a feasible and practically achievable alternative for the electrolyte sealing difficulties that have been associated with bipolar batteries while also providing other advantages.
The patent art includes several examples of battery arrangements. Included in this art is the patent of Brijesh Vyas, U.S. Pat. No. 4,471,038, which concerns a nickel-cadmium battery improved through the addition of organic polymer compounds to one of the battery electrodes. This art also includes the patent of Margaret A. Reid, U.S. Pat. No. 4,439,465, which concerns a method for making a lightweight substrate or plaque usable in a battery or fuel cell.
The U.S. patent of Claude J. Menard, U.S. Pat. No. 4,154,908, concerns an electrode configuration for alkaline batteries wherein shapes enabling use of unequal amounts of electrode material on the electrodes of different polarity are provided in order to obtain improved battery cycle life and superior volumetric energy density. The Menard patent principally concerns silver-zinc, silver-cadmium, and nickel-zinc batteries and teaches the use of potassium hydroxide as an electrolyte. This patent is also concerned with increasing the number of discharge cycles and the depth of discharge endurance characteristics of a battery. The Menard patent is also concerned with electrode shape change or the migration of active material between different regions of an electrode.
The patent of Gunter Gutmann, U.S. Pat. No. 4,215,184, concerns an improved cell arrangement for nickel-oxide/hydrogen battery cells which achieves improves heat transfer in the axial direction of the battery cell through a reduction of the number of elements in a cell stack.
The patent of David H. Fritts et al, U.S. Pat. No. 4,242,179, concerns a method for fabricating cadmium electrodes usable in nickel-cadmium and silver-cadmium batteries, for example. The Fritts patent achieves an improved dual loading of the cadmium material without surface buildup and eliminates some of the electrode processing steps previously required. The disclosure of the Fritts patent is incorporated herein by reference.
The patent of C. R. Walk et al, U.S. Pat. No. 3,746,940, concerns a cadmium coulometer of the non-aqueous type--an electrolytic cell device usable for such non-battery purposes as measuring plating accomplishment, as an electroplating cell, or for timing purposes. The electrolytic nature and the electrolytic cell enclosure of the Walk patent are in some ways similar to battery structures.